The present invention relates to alternating current (xe2x80x9ca.c.xe2x80x9d) or direct current (xe2x80x9cd.c.xe2x80x9d) generators, alternators, and motors and, more particularly, to a technique for cooling the rotors of such equipment.
The windings of equipment, such as generators, alternators and motors, whether a.c. or d.c., must be maintained below some predetermined temperature for proper operation. If not, the insulating material used on the windings will degrade and adversely affect the operation of such equipment. To avoid such degradation, either the current flowing through the windings must be reduced or the heat dissipation capabilities of the equipment must be enhanced. Reducing the current flowing through the windings results in a corresponding power output reduction that is often not compatible with many applications. Accordingly, there has been considerable attention to the development of techniques for enhancing the cooling capabilities of the windings, whether such windings are in the rotor or the stator.
One technique for enhancing heat dissipation in electrical equipment, such as generators, alternators and motors, is to add fins and heat sinks to the equipment. This technique while providing satisfactory results increases both the weight and size of the equipment. It is therefore not suitable for applications, such as aircraft and military applications, where changes in the equipment design must confirm to stringent size and weight constraints. Another technique to increase the heat dissipation capabilities of electrical equipment having windings is to incorporate fluid cooling. In one approach, a cooling fluid is circulated through the equipment housing and rotor shaft. This reduces the temperature of the stator windings but does not substantially reduce the rotor winding temperature. In another technique, the temperature of the rotor winding is reduced by spraying a cooling medium onto the rotor, as it is spinning. The sprayed medium has associated contamination and shorting problems and is not suitable for certain applications. More recently, as disclosed in U.S. Pat. No. 4,943,746 entitled xe2x80x9cLiquid Cooled Salient Pole Rotor Support Wedgesxe2x80x9d to Scherzineger et al., issued Jul. 24, 1990, a liquid medium is conducted through support wedges disposed between each pole of a multi-pole rotor. While this technique serves to reduce the temperature of the rotor winding, it does not cool all of the winding and, does not effectively cool the poles. As a result, it can not provide sufficient rotor cooling for applications requiring certain power output levels from equipment having given size and weight. Accordingly, it would be highly desirable if a technique could be developed that would enhance the cooling of rotor windings in a manner that reduces the size and weight and increases the power output.
The present invention relates to the cooling of a rotor in a generator, alternator or motor, either a.c. or d.c., having at least one rotor and wherein the rotor has at least two poles. In accordance with the present invention, one or more xe2x80x9ccold platexe2x80x9d elements are disposed between the rotor poles and the windings encircling those poles. Each element is preferably fabricated of a material having high thermal conductivity. In the preferred embodiment, each element incorporates one or more passageways for conducting a cooling medium therethrough so as to increase the cooling provided to the surrounding rotor and windings.
In the disclosed embodiment of the present invention, each element engages with a mating element and the resulting pair encircles a rotor pole. The inner surface of each element, i.e., the surface of the element adjacent to the rotor pole, is advantageously shaped so that this entire surface is in contact with the pole. This maximizes the conductive heat transfer from the rotor pole to each element. In addition, the outer surface of each element, i.e., the surface of the element adjacent to the winding encircling that pole, is advantageously shaped so that this entire surface is in contact with the winding. This maximizes the conductive heat transfer coupled from the winding to each element surrounded by that winding.
The use of the element described above advantageously cools both the poles and the windings and does so in a manner that does not increase the size of the overall motor or generator assembly. Accordingly, the present invention is adaptable to both new or existing generator, alternator or motor designs. In addition, it can be utilized in any such equipment having any number of rotor poles.